The overall goal of the proposed experiments is to investigate the cellular and molecular mechanisms of synapse formation within the cerebral cortex. The fundamental questions of synaptogenesis are how a growth cone is transformed into a presynaptic terminal and how a postsynaptic specialization forms opposite a presynaptic terminal. This study will focus on the development of the presynaptic side of the synapse, about which very little is known. Because the evolution of an axonal growth cone into a presynaptic terminal is a highly dynamic process, the proposed experiments will make use of a novel, real-time approach to examine simultaneously the morphological and physiological changes that occur as a synapse forms. To do this, time-lapse confocal imaging will be combined with patch-clamp recording from single, identifiable synapses and growth cones of cultured cortical neurons. Changes in membrane dynamics, protein trafficking, and synaptic transmission will be explored. The results of these experiments will not only significantly improve the current understanding of normal brain development, but also have implications for treatment of neurodevelopmental disorders and numerous neurological disorders characterized by synaptic loss.